Scientists explain the origin of the fast radio burst

Radio bursts are short and bright bursts of radio waves produced by highly entangled objects such as neutron stars and black holes. These temporary flares last only a thousandth of a second and can carry enormous amounts of energy—enough to briefly go through entire galaxies.

Since the first radio burst (FRB) was discovered in 2007, astronomers have detected thousands of FRBs, whose locations range from within our galaxy to distances up to 8 billion light-years. Exactly how these cosmic radio fires are started is largely unknown.

Now, MIT astronomers have pinpointed the origin of another fast radio burst using a new technique that can do the same for other FRBs. In their new study, which appears in the journal Naturethe team focused on FRB 20221022A—a fast radio burst detected in a galaxy about 200 million light-years away.

The team went on to find the exact location of the radio by examining its “scintillation”, similar to how stars twinkle in the night sky. Scientists studied the bright changes in the FRB and concluded that the burst must have originated near its source, rather than farther away, as some models had predicted.

The team estimates that FRB 20221022A erupted from very close to an orbiting neutron star, roughly 10,000 kilometers away. It is less than the distance between New York and Singapore. At such close proximity, it is possible that the explosion occurred in the neutron star’s magnetosphere—the extremely strong magnetic field surrounding the star.

The team’s findings provide the first solid evidence that fast radio bursts can occur in the magnetosphere, the strongly magnetic environment immediately surrounding a highly coherent object.

“In these neutron stars, the gravity is really at the limits of what the universe can produce,” says lead author Kenzie Nimmo, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research. “There has been a lot of debate about whether this bright radio could even escape that extreme plasma.”

“Around these powerful neutron stars, also known as magnetars, atoms would not exist—they would be pulled apart by gravity,” says Kiyoshi Masui, assistant professor of physics. MIT.

“The exciting thing here is, we find that the energy stored in those magnetic fields, close to the source, twists and rearranges itself so that it can be released as radio waves that we can see half of the universe.”

The MIT authors of the study include Adam Lanman, Shion Andrew, Daniele Michilli, and Kaitlyn Shin, as well as colleagues from several institutions.

The size of the explosion

The discovery of fast radio bursts has increased in recent years, thanks to Canada’s Hydrogen Intensity Mapping Experiment (CHIME). A radio telescope array consists of four large, upright amocei, each shaped like a half-pipe, arranged to detect radio emissions through among the types that are relatively easy to explode quickly.

As of 2020, CHIME has discovered thousands of FRBs from across the universe. While scientists generally believe that bursts occur in very dense matter, the physics that actually drive FRBs is unclear.

Some models predict that the fast radio burst should originate in the immediately perturbed magnetosphere surrounding the compact object, while others predict that the burst should be start at a distance, as part of a moving wave that propagates away from the central object.

In order to distinguish between these two conditions, and to determine the source of the fast radio burst, the team considered scintillation—the effect of light from a small bright source such as a star, filters through a certain region, such as the gas of a galaxy.

As the starlight passes through the gas, it bends in ways that make it appear to a distant observer, as if the star were twinkling. The smaller or farther away an object is, the brighter it is. Light from larger or closer objects, such as the planets in our solar system, is bent less, so it doesn’t appear as bright.

The team reasoned that if they could estimate the frequency of the FRB, they could determine the approximate size of the region where the FRB originates. The smaller the area, the closer the burst would be to its source, and the more likely it would be from a disturbed magnetic environment. The larger the distance, the farther the burst will be, lending support to the idea that FRBs come from distant branches.

Sparkling pattern

To test their hypothesis, the researchers looked at FRB 20221022A, a fast radio burst detected by CHIME in 2022. The signal lasts about two milliseconds, and it’s a fairly run-of-the-mill FRB, given its brightness.

However, colleagues at McGill University found that FRB 20221022A exhibited one unique property. The light from the burst was highly polarized, with the direction of polarization following a smooth S-shaped curve. This pattern is interpreted as evidence that the FRB region is rotating—a feature that has previously been seen in pulsars, which are very energetic, rotating neutron stars.

Seeing the same polarization as a fast radio burst was a first, suggesting that the signal might be coming from the vicinity of a neutron star. The McGill team’s results are reported in an accompanying paper at Nature.

The MIT team realized that if FRB 20221022A came from near a neutron star, they should be able to prove this, using scintillation.

In their new study, Nimmo and his colleagues analyzed the data from CHIME and saw strong variations in brightness that indicated scintillation—in other words, the FRB was sparkling. They confirmed that there is gas somewhere between the telescope and the FRB that bends and filters the radio waves.

The team then determined where this gas could be found, which confirmed that the gas in the FRB galaxy was responsible for the observed scintillation. This gas acted as a natural lens, allowing researchers to zoom in on the FRB site and detect the burst from a very small area, estimated to be 10,000 kilometers across.

“This means that the FRB is probably within hundreds of thousands of kilometers from the source,” Nimmo says. “That’s pretty close. By comparison, we’d expect the signal to be over tens of millions of kilometers away if it came from a shockwave, and we wouldn’t see any scintillation at all.” .”

“Getting close to 10,000 kilometers, 200 million light-years away, is like being able to measure the diameter of a DNA helix, which is about 2 nanometers across,” says Masui. over the moon,” Masui says. “There’s an incredible range of scales involved.”

The team’s results, combined with findings from the McGill team, highlight the possibility that FRB 20221022A originated at the edges of a compact object. Instead, research proves for the first time that fast radio bursts can occur near a neutron star, in highly disturbed magnetic fields.

“These explosions happen regularly, and CHIME detects them several times a day,” Masui says. “There may be many different types of how and where they occur, and this scintillation method will be very useful in helping to disentangle the different physics that drive the explosion. right.”

This story is republished with permission from MIT News (web.mit.edu/newsoffice/), a popular site covering news about MIT research, innovation and education.